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I need to call gpio_get_value, gpio_set_value, gpio_direction_input/output in my driver, and there is a timing requirement that requests the function calls to be returned in less than 5us time.

Can gpiolib meet this requirement or is it not deterministic? If not, what could be the solution? directly accessing GPIO registers?

Thanks a lot.

spitfire88
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user1697356
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  • Did you try calling the gpio_xxx() API on you device and profile the time taken? Are the results deterministic enough?... – TheCodeArtist Oct 16 '12 at 16:55

1 Answers1

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Calling one of that functions involves executing a linux kernel function, thus there are at least two context switches: one to run kernel code and one to come back to userland.

These switches can mean some time can get wasted if interrupts or signal come in to be executed.

Anyways if you need deterministic time deadlines you need to switch to a real-time patched kernel Real Time linux wiki homepage

I don't know if 5us is feasible, it depends on the system load, on the active drivers (e.g. there's a read/write filesystem?), but you can test.

Fabio Pozzi
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  • Yes, however if the requirement is simply that the sequence of operations complete within a certain amount of time from when it begins (but the latency of beginning is not important), then doing all three operations in immediate sequence from within the kernel in a non-preemtable context could be sufficient. But if the actual timing of the operations is required, then real time extensions are likely needed. – Chris Stratton Dec 06 '12 at 15:20
  • I agree with you @ChrisStratton. The thing is that the three function listed are the three function used to interface with gpios to set/get a value and to get info about the pin config so I thought they would be called in different instants of time, not in direct sequence. – Fabio Pozzi Dec 06 '12 at 16:10